Systems and methods for achieving best effort home route capacity on protection paths during optical restoration

ABSTRACT

Systems and methods of optical restoration include, with a photonic service (14), in an optical network (10, 100), operating between two nodes (A, Z) via an associated optical modem (40) at each node, wherein each modem (40) is capable of supporting variable capacity, C1, C2, . . . , CN where C1&gt;C2&gt; . . . &gt;CN, detecting a fault (16) on a home route of the photonic service (14) while the photonic service (14) operates at a home route capacity CH, CH is one of C1, C2, . . . , CN−1; downshifting the photonic service (14) to a restoration route capacity CR, CR is one of C2, C3 . . . , CN and CR&lt;CH; switching the photonic service (14) from the home route to a restoration route (18) while the photonic service (14) operates at a restoration route capacity CR; and monitoring the photonic service (14) and copropagating photonic services during operation on the restoration route (18) at the restoration route capacity CR for an upshift of the photonic service (14).

FIELD OF THE DISCLOSURE

The present disclosure generally relates to optical networking. Moreparticularly, the present disclosure relates to systems and methods forachieving best effort home route capacity on protection paths duringoptical restoration.

BACKGROUND OF THE DISCLOSURE

Optical (photonic) networks and the like (e.g., Dense WavelengthDivision Multiplexed (DWDM)) are deploying control plane systems andmethods. Control planes provide automatic allocation and management ofnetwork resources in an end-to-end manner. Example control planes mayinclude Automatically Switched Optical Network (ASON) as defined inITU-T G.8080/Y.1304, Architecture for the automatically switched opticalnetwork (ASON) (02/2005), the contents of which are herein incorporatedby reference; Generalized Multi-Protocol Label Switching (GMPLS)Architecture as defined in IETF Request for Comments (RFC): 3945(10/2004) and the like, the contents of which are herein incorporated byreference; Optical Signaling and Routing Protocol (OSRP) from CienaCorporation which is an optical signaling and routing protocol similarto PNNI (Private Network-to-Network Interface) and MPLS; or any othertype control plane for controlling network elements at multiple layers,and establishing connections therebetween. Control planes are configuredto establish end-to-end signaled connections such as SubnetworkConnections (SNCs) in ASON or OSRP, and Label Switched Paths (LSPs) inGMPLS and MPLS.

In addition to control planes which are distributed, a centralizedmethod of control exists with Software Defined Networking (SDN) whichutilizes a centralized controller. SDN is an emerging framework whichincludes a centralized control plane decoupled from the data plane. SDNprovides the management of network services through abstraction oflower-level functionality. This is done by decoupling the system thatmakes decisions about where traffic is sent (the control plane) from theunderlying systems that forward traffic to the selected destination (thedata plane). Note, distributed control planes can be used in conjunctionwith centralized controllers in a hybrid deployment. SDN and controlplanes are configured to compute paths, to route/signal the SNCs/LSPs,and program the underlying hardware accordingly.

Optical (photonic) networks include various Optical Add/Drop Multiplexer(OADM) nodes interconnected by optical links which can include in-lineoptical amplifiers. An Optical Multiplex Section (OMS) is a networksection between two OADMs where spectral loading is constant on allspans. Photonic networks use control planes, SDN, etc. to providerestoration (also referred to as protection) which is a key feature innetworks where a backup (protection) path takes over for an active(working) path of a service or call when there is a failure in theactive path. Conventionally, photonic services are engineered to operatean associated modulation format which provides a specific amount ofbandwidth based on a plurality of factors which determine optical marginbased on End of Life (EOL) conditions. With respect to restoration,responsive (or before) a fault affecting a photonic service, aprotection path is determined to route the faulted photonic service.

Conventionally, the protection path is constrained to support the marginrequirements of the photonic service from its home route (i.e., theoriginally computed path, the working path). Next-generation opticalmodems support adaptive bandwidth via adaptable modulation formats andbaud rates. These advanced features add complexity to the protectionroute computation and systems and methods are needed to support unequalbandwidth rates on protection routes while a photonic service is off ofits home route.

BRIEF SUMMARY OF THE DISCLOSURE

In an embodiment, a method of optical restoration includes, in anoptical network with a photonic service operating between two nodes viaan associated optical modem at each node, wherein each modem is capableof supporting variable capacity, C₁, C₂, . . . , C_(N) where C₁>C₂> . .. >C_(N), detecting a fault on a home route of the photonic servicewhile the photonic service operates at a home route capacity C_(H),C_(H) is one of C₁, C₂, . . . , C_(N−1); downshifting the photonicservice to a restoration route capacity C_(R), C_(R) is one of C₂, C₂ .. . , C_(N) and C_(R)<C_(H); switching the photonic service from thehome route to a restoration route while the photonic service operates ata restoration route capacity C_(R); and monitoring the photonic serviceduring operation on the restoration route at the restoration routecapacity C_(R) for an upshift.

The method can further include, responsive to a determination that thephotonic service can upshift from the restoration route capacity C_(R)on the restoration route, the determination based at least on margin ofthe photonic service on the restoration route, configuring theassociated modems to operate at an upshifted capacity from therestoration route capacity C_(R). The method can further include,responsive to a determination that the photonic service can upshift fromthe restoration route capacity C_(R) on the restoration route, thedetermination based at least on margin of the photonic service on therestoration route and based on margin of all copropagating photonicservices over at least a portion of the restoration route, configuringthe associated modems to operate at an upshifted capacity from therestoration route capacity C_(R).

The monitoring can include measuring Bit Error Rate (BER) of thephotonic service on the restoration route to determine margin in termsof Signal-to-Noise Ratio (SNR). The SNR margin of the photonic servicecan be determined by considering a minimum of a time-series lower boundfrom all associated modems of the photonic service. The photonic servicecan be upshifted if the margin at the restoration route capacity C_(R)is higher than an SNR margin to overcome a signal degrade condition at aC_(R+1). The method can further include determining the restorationroute utilizing path computation via one or more of a control plane, aSoftware Defined Networking (SDN) controller, a Network ManagementSystem (NMS), and a Path Computation Engine (PCE). The method canfurther include determining viable capacity on the restoration route andperforming the downshifting based thereon.

The optical network can be a mesh network with a plurality of nodesinterconnected by a plurality of links and with a plurality of opticalsections. The restoration route can have more link budget constraintsthan the home route, for which the home route capacity is estimated tobe not achievable in end of life. The method can further includerestoring to a path with home route capacity, C_(H) if viable capacityon the restoration route is not known in advance, and then downshiftingto a next available capacity, C_(H−1) if the photonic service fails torun error-free and no fault on the restoration route can be correlatedwith the failure to run error-free.

In another embodiment, a node in an optical network includes one or moremodems configured to connect to the optical network and to provide aphotonic service with a second node in the optical network, wherein eachmodem is capable of supporting variable capacity, C₁, C₂, . . . , C_(N)where C₁>C₂> . . . >C_(N); and a controller connected to the one or moremodems and configured to detect or receive a fault on a home route ofthe photonic service while the photonic service operates at a home routecapacity C_(H), C_(H) is one of C₁, C₂, . . . , C_(N−1), cause adownshift of the photonic service to a restoration route capacity C_(R),C_(R) is one of C₂, C₂ . . . , C_(N) and C_(R)<C_(H), cause a switch ofthe photonic service from the home route to a restoration route whilethe photonic service operates at a restoration route capacity C_(R), andmonitor the photonic service during operation on the restoration routeat the restoration route capacity C_(R) for an upshift.

The controller can be further configured to determine the photonicservice can upshift from the restoration route capacity C_(R) based onmargin of the photonic service on the restoration route, and, responsiveto a determination that the photonic service can upshift from therestoration route capacity C_(R) on the restoration route, configure theassociated modem to operate at an upshifted capacity from therestoration route capacity C_(R). The controller can be furtherconfigured to determine the photonic service can upshift from therestoration route capacity C_(R) based on margin of the photonic serviceon the restoration route and based on margin of all copropagatingphotonic services over all or a portion of the restoration route; and,responsive to a determination that the photonic service can upshift fromthe restoration route capacity C_(R) on the restoration route, configurethe associated modem to operate at an upshifted capacity from therestoration route capacity C_(R).

The photonic service can be monitored based on measurements of Bit ErrorRate (BER) of the photonic service on the restoration route to determinemargin in terms of Signal-to-Noise Ratio (SNR). The photonic service canbe upshifted if the margin at the restoration route capacity C_(R) ishigher than an SNR margin to overcome a signal degrade condition at aC_(R+1). The controller can be further configured to determine therestoration route utilizing path computation via one or more of acontrol plane, a Software Defined Networking (SDN) controller, a NetworkManagement System (NMS), and a Path Computation Engine (PCE). Thecontroller can be further configured to determine viable capacity on therestoration route and perform the downshift based thereon. The opticalnetwork can be a mesh network with a plurality of nodes interconnectedby a plurality of links and with a plurality of optical sections.

In a further embodiment, an optical network includes a plurality ofnodes; and a plurality of links interconnecting the plurality of nodesin a mesh network, wherein at least one photonic service operatesbetween two nodes via an associated optical modem at each node, whereineach modem is capable of supporting variable capacity, C₁, C₂, . . . ,C_(N) where C₁>C₂> . . . >C_(N), wherein, responsive to detection of afault on a home route of the at least one photonic service while thephotonic service operates at a home route capacity C_(H), C_(H) is oneof C₁, C₂, . . . , C_(N−1), the at least one photonic service isdownshifted to a restoration route capacity C_(R), C_(R) is one of C₂,C₂ . . . , C_(N) and C_(R)<C_(H), and the at least one photonic serviceis switched from the home route to a restoration route while thephotonic service operates at a restoration route capacity C_(R), andwherein the at least one photonic service is monitored during operationon the restoration route at the restoration route capacity C_(R) for anupshift.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated and described herein withreference to the various drawings, in which like reference numbers areused to denote like system components/method steps, as appropriate, andin which:

FIG. 1 is a network diagram of a photonic network with Optical Add/DropMultiplexer (OADM) nodes A, B, C, D, E, F and intermediate amplifiers;

FIG. 2 is a network diagram of the photonic network of FIG. 1 with thephotonic service downshifted in capacity on the protection path;

FIG. 3 is a network diagram of a portion of a mesh network;

FIG. 4 is a network diagram illustrating modems forming a photonicservice between OADMs;

FIG. 5 is a network diagram of an example optical network with fiveinterconnected sites;

FIG. 6 is a block diagram of a node for use with the systems and methodsdescribed herein;

FIG. 7 is a block diagram of a controller to provide control planeprocessing and/or OAM&P for the node of FIG. 7 ;

FIG. 8 is a flowchart of an upshift process for restoring a photonicservice from a home route to a restoration route with some insight intomargin available on the restoration route;

FIG. 9 is a flowchart of a downshift process for restoring a photonicservice from a home route to a restoration route without insight intomargin available on the restoration route;

FIG. 10 is a flowchart of a process including both upshifting anddownshifting of capacity when moving to a restoration route from a homeroute;

FIG. 11 is a flowchart of a detailed upshift process which providesadditional details of the upshift process of FIG. 8 ;

FIG. 12 is a flowchart of a detailed downshift process which providesadditional details of the downshift process of FIG. 9 ;

FIG. 13 is a flowchart of an upshift capability process which determinesthe margin and possibility of an upshift in the aforementionedprocesses; and

FIG. 14 is a graph of an example photonic service illustratingSignal-to-Noise (SNR) in dB versus Bit Error Rate (BER) for differentcapacity rates, namely 100G, 200G, 300G, 400G; and

FIG. 15 is a flowchart of a process for determining SNR margins forother photonic services sharing the same path as the photonic service.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to systems and methods for achieving homeroute capacity via best effort during optical restoration. The systemsand methods eliminate the strong dependency on margin prediction duringphotonic service restoration and hence, ease off the capacity predictionrequirement before switching to a restoration route in a complex meshnetwork environment where system dynamics are constantly evolving.Instead, the systems and methods utilize existing margins aftersuccessful restoration. In other words, the systems and methods adaptservice capacity to available margins to get home route capacity in abest-effort approach in a non-service affecting way (i.e., withoutimpacting any other co-propagating services that may already be runningwith low margins and/or with up-shifted capacity). The systems andmethods contemplate operation in mesh optical networks where variousphotonic services can operate over different sections, leading to acomplex environment. Instead of requiring knowledge and certainty ofmargins on restoration routes, the systems and methods utilize a switchfirst approach and then adapts capacity to the best available marginconsidering current spectral fill condition. This allows the services tobest utilize the current available steady-state of the networkconditions.

Photonic Network

FIG. 1 is a network diagram of a photonic network 10 with OADM nodes A,B, C, D, E, F and intermediate amplifiers 12. The photonic network 10can implement a control plane, be controlled by SDN, etc. The photonicnetwork 10 includes a photonic service 14 operating on a working path(also referred to as a home route) between nodes A, B, Z with a capacityof C₁. The working path was computed and set for the capacity of C₁. Thephotonic service 14 is formed by modems (Tx/Rx) that are capable ofsupporting various capacity rates such as C₁, C₂, . . . , C_(N), whereC₁>C₂> . . . >C_(N). Responsive to a fiber cut 16, the photonic service14 is restored on a restoration route 18 between nodes A, C, D, E, Z,where the capacity on the home route C_(H) (which is equal to C₁) willnot be viable at End of Life (EOL). EOL is typically simulated forfull-fill spectrum condition at all OMS (from OADM to OADM), consideringstatistical aging penalties from all components and fiber plants in thepath, plus repair margins for all fiber spans. Note, as describedherein, the terms route and path are equivalent and denote a series oflinks in the network 10 for a specific photonic service.

However, assumptions considered for EOL condition may not match therestoration route 18 condition, considering spectral fill, aging andrepair margins per spans and so on that always leaves rooms for addingadditional margins and, hence, additional capacity even though thecapacity used at the home route cannot be achieved at EOL on therestoration route 18. The question is how to determine if those channelscan be operated at a higher capacity than their predicted EOL ratefollowing restoration in a dynamic mesh-environment, where spectral-fillat each OMS is evolving over time.

FIG. 2 is a network diagram of the photonic network 10 with the photonicservice downshifted in capacity on the restoration route 18. Fromoffline or on-line link budget estimation, the control plane or anexternal agent knows the available Signal-to-Noise Ratio (SNR) marginand the maximum capacity that can be viable on a path at the EOLcondition (full-fill spectrum+aging penalties+repair margins). The EOLcondition guarantees the viable capacity for a service for a given pathbased on inputs used for planning or for link budget estimation. Atrestoration, the EOL capacity value for the new restoration route ispushed to the modems if the EOL capacity<the home route capacity themodems were carrying. The modems switch to the EOL capacity and drop therest based on pre-defined priority list for traffic slots. For example,if service is running at 400 Gbps capacity at the home route and theonly available restoration route is capable of carrying 200 Gbps at EOL,then at restoration, modems are switched at 200 Gbps, dropping the other200 Gbps.

The modem pairs per photonic service stay at down-shifted line rate(capacity) until the home route is fixed or another path with higherline rate becomes viable. Since fixing faults in fiber plants may takedays, weeks or months, which means, the modems can potentially stay atthe downshifted rate for a prolonged period of time. There areapproaches that can predict SNR margin for a service to a new pathbefore it is being switched to that path only if the channel spectrumstate before and after the switch remain finite. That is, the algorithmknows the current spectral fill state and knows exactly where the newservices will show up in the restoration route at what power level andmodulation formats after the restoration. That implies, if only thenetwork's working and restoration routes are very much linear, andspectral states are very much known before and after a fiber fault andrestoration, these approaches can predict the exact SNR margin that willbe available on the restoration route at its current condition (notend-of-life), and can switch the modems to a higher than EOL line ratethat can remain viable until the home-route is fixed.

FIG. 3 is a network diagram of a mesh network 30. In a mesh networkenvironment, when channels will be restored to a path from differentother paths in the network at a different time-scale for a single ormultiple fiber cuts, it is hard to predict what the final channelpopulation (spectral file and specific fill locations within thespectrum) will be in every OMS for a given path of interest. The problemin spectral fill prediction is already complicated in fixed grid network(where all photonic services are greater than 50 GHz and on a grid). Theproblem is even worse for flexible grid networks where restoringphotonic services can be of different spectral widths (12.5 GHz˜500GHz).

Hence, it is hard to predict the final spectral state before restorationeven takes place, and hence, most conventional approaches focus onpredicting margins for full-fill spectral conditions, leaving additionalmargins unused for services. There are other approaches that again cansimulate the network in steady-state considering no more change incurrent conditions and steal margins from some services and give moremargins to others to up-shift them to higher capacity. Again, theseapproaches do not take restoration events into account, and cannot tellif enough margin will be available if the up-shifted services arerestored to a different path. Hence, the challenge remains how onrestoration can take advantage of available margins on the path toachieve home route capacity at best effort until the home route isfixed.

Modems

FIG. 4 is a network diagram illustrating modems 40A, 40B forming aphotonic service 42 between OADMs 44A, 44B, 44C. In this example, theOADMs 44A, 44C are add/drop locations and the OADM 44B is an expressnode. Each modem 40A, 40B can be tunable so that it can selectivelygenerate a wavelength centered at the desired carrier wavelength (orfrequency). The modem 40A, 40B can support multiple coherent modulationformats such as, for example, i) dual-channel, dual-polarization (DP)binary phase-shift keying (BPSK) for 100G at submarine distances, ii) DPquadrature phase-shift keying (QPSK) for 100G at ultra long-hauldistances, iii) 16-quadrature amplitude modulation (QAM) for 200G atmetro to regional (600 km) distances), iv) dual-channel 16QAM for 400Gat metro to regional distances, v) dual-channel 64QAM for 800G at metroto regional distances. Thus, in an embodiment, the same modem 40 cansupport 100G to 800G. With associated digital signal processing (DSP) inthe modem 40 hardware, moving from one modulation format to another iscompletely software-programmable.

The modem 40 can also support N-QAM modulation formats with and withoutdual-channel and dual-polarization where N can even be a real number andnot necessarily an integer. Here, the modem 40 can support non-standardspeeds since N can be a real number as opposed to an integer, i.e., notjust 100G, 200G, or 400G, but variable speeds, such as 130G, 270G, 560G,etc. These rates could be integer multiples of 10 Gb/s, or of 1 Gb/s.Furthermore, with the DSP and software programming, the capacity of theflexible optical modem can be adjusted upwards or downwards in a hitlessmanner so as to not affect the guaranteed rate. Additionally, the modems40 can tune and arbitrarily select spectrum; thus, no optical filtersare required. Additionally, the modem 40 can support various aspects ofnonlinear effect mitigation and dispersion compensation (both forchromatic and polarization mode) in the electrical domain, thuseliminating external dispersion compensation devices, filters, etc.Modems can also adapt the forward error correction coding that is used,as another method to trade-off service rate versus noise tolerance. Ingeneral, the bit rate of the service provided by a modem is proportionalto the amount of spectrum occupied and is a function of the noisetolerance.

Optical Network

FIG. 5 is a network diagram of an example optical network 100 with fiveinterconnected sites 110 a, 110 b, 110 c, 110 d, 110 e. The sites 110are interconnected by a plurality of links 120. Each of the sites 110can include a switch 122 and one or more Wavelength Division Multiplexed(WDM) network elements 124. The switch 122 is configured to provideservices at Layer 0 (DWDM, photonic), Layer 1 (e.g., Optical TransportNetwork (OTN)), and/or Layer 2 (e.g., Ethernet). The WDM networkelements 124 provide the photonic layer (i.e., Layer 0) and variousfunctionality associated therewith (e.g., multiplexing, amplification,optical routing, wavelength conversion/regeneration, local add/drop,etc.) including photonic control. Of note, while shown separately, thoseof ordinary skill in the art would understand the switch 122 and the WDMnetwork elements 124 may be realized in the same network element or eachin multiple network elements. The photonic layer can also includeintermediate amplifiers and/or regenerators on the links 120 which areomitted for illustration purposes. The optical network 100 isillustrated, for example, as an interconnected mesh network, and thoseof ordinary skill in the art will recognize the optical network 100 caninclude other architectures, with additional sites 110 or with fewersites 110, with additional network elements and hardware, etc. Theoptical network 100 is presented herein as an example of implementingthe optical restoration systems and methods.

The sites 110 communicate with one another optically over the links 120.The sites 110 can be network elements which include a plurality ofingress and egress ports forming the links 120. Further, the sites 110can include various degrees, i.e., the site 110 c is a one-degree node,the sites 110 a, 110 d are two-degree nodes, the site 110 e is athree-degree node, and the site 110 b is a four-degree node. The numberof degrees is indicative of the number of adjacent nodes 130 at eachparticular node 130. As described herein, the terms node and networkelement are interchangeable, each representing a device in the network100. The network 100 includes a control plane 126 operating on and/orbetween the switches 122 and/or the WDM network elements 124 at thesites 110 a, 110 b, 110 c, 110 d, 110 e. The control plane 126 includessoftware, processes, algorithms, etc. that control configurable featuresof the network 100, such as automating discovery of the switches 122,capacity of the links 120, port availability on the switches 122,connectivity between ports; dissemination of topology and bandwidthinformation between the switches 122; calculation and creation of pathsfor connections; network level protection and restoration; and the like.In an embodiment, the control plane 126 can utilize AutomaticallySwitched Optical Network (ASON), Generalized Multiprotocol LabelSwitching (GMPLS), Optical Signal and Routing Protocol (OSRP) (fromCiena Corporation), or the like. Those of ordinary skill in the art willrecognize the optical network 100 and the control plane 126 can utilizeany type control plane for controlling the switches 122 and/or the WDMnetwork elements 124 and establishing connections.

An SDN controller 128 can also be communicatively coupled to the opticalnetwork 100. SDN is a framework which includes a centralized controlplane decoupled from the data plane. SDN provides the management ofnetwork services through abstraction of lower-level functionality. Thisis done by decoupling the system that makes decisions about wheretraffic is sent (the control plane) from the underlying systems thatforward traffic to the selected destination (the data plane). SDN workswith the SDN controller 128 knowing a full network topology throughconfiguration or through the use of a controller-based discovery processin the optical network 100. The SDN controller 128 differs from amanagement system in that it controls the forwarding behavior of thenodes 122, 124 only, and performs control in real time or near realtime, reacting to changes in services requested, network trafficanalysis and network changes such as failure and degradation. Also, theSDN controller 128 provides a standard northbound interface to allowapplications to access network resource information and policy-limitedcontrol over network behavior or treatment of application traffic. TheSDN controller 128 sends commands to each of the nodes 122, 124 tocontrol matching of data flows received and actions to be taken,including any manipulation of packet contents and forwarding tospecified egress ports.

Example Network Element/Node

FIG. 6 is a block diagram of a node 130 for use with the systems andmethods described herein. The node 130 can be the switch 122, the WDMnetwork element 124, or the like. In an embodiment, the node 130 can bea network element that may consolidate the functionality of aMulti-Service Provisioning Platform (MSPP), Digital Cross-Connect (DCS),Ethernet and/or Optical Transport Network (OTN) switch, Wave DivisionMultiplexed (WDM)/Dense WDM (DWDM) platform, Packet Optical TransportSystem (POTS), etc. into a single, high-capacity intelligent switchingsystem providing Layer 0, 1, 2, and/or 3 consolidation. In anotherembodiment, the node 130 can be any of an OTN Add/Drop Multiplexer(ADM), a Multi-Service Provisioning Platform (MSPP), a DigitalCross-Connect (DCS), an optical cross-connect, a POTS, an opticalswitch, a router, a switch, a Wavelength Division Multiplexing (WDM)terminal, an access/aggregation device, etc. That is, the node 130 canbe a system with ingress and egress digital signals and switching ofchannels, timeslots, tributary units, etc. Also, the node 130 can be asystem with ingress and egress of optical signals and switching/routingof wavelengths. Of course, the node 130 can combine both digital signalsand optical signals. While the node 130 is generally shown as an opticalnetwork element, the systems and methods contemplated for use with anyswitching fabric, network element, or control plane network basedthereon, supporting Layer 0 (photonic) restoration.

The node 130 can include common equipment 132, one or more line modules134, and one or more switch modules 136. The common equipment 132 caninclude power; a control module; Operations, Administration,Maintenance, and Provisioning (OAM&P) access; user interface ports; andthe like. The common equipment 132 can connect to a management system138 through a data communication network 140 (as well as a PathComputation Element (PCE), the SDN controller 128, OpenFlow controller,etc.). The management system 138 can include a Network Management System(NMS), Element Management System (EMS), or the like. Additionally, thecommon equipment 132 can include a control plane processor, such as acontroller 150 illustrated in FIG. 7 configured to operate the controlplane 126, the SDN controller 128 as described herein. The node 130 caninclude an interface 142 for communicatively coupling the commonequipment 132, the line modules 134, and the switch modules 136 to oneanother. For example, the interface 142 can be a backplane, midplane, abus, optical or electrical connectors, or the like. The line modules 134are configured to provide ingress and egress to the switch modules 136and to external connections on the links to/from the node 130. Otherconfigurations and/or architectures are also contemplated.

The line modules 134 can include the optical modems 40. The line modules134 support the photonic services which can include a protocol, such as,for example, ODUn, ODUflex, OTUCn, Flexible Ethernet, etc. Further, theline modules 134 can include a plurality of optical connections permodule and each module may include a flexible rate support for any typeof connection, such as, for example, 155 Mbps, 622 Mbps, 1 Gbps, 2.5Gbps, 10 Gbps, 40 Gbps, 100 Gbps, 200 Gbps, 400 Gbps, N×1.25 Gbps, andany rate in between as well as higher rates. The line modules 134 caninclude wavelength division multiplexing interfaces, short reachinterfaces, and the like, and can connect to other line modules 134 onremote network elements, end clients, edge routers, and the like, e.g.,forming connections on the links in the network 100. From a logicalperspective, the line modules 134 provide ingress and egress ports tothe node 130, and each line module 134 can include one or more physicalports. The switch modules 136 are configured to switch channels,timeslots, tributary units, packets, etc. between the line modules 134.For example, the switch modules 136 can provide wavelength granularity(Layer 0 switching); OTN granularity; Ethernet granularity; and thelike. Specifically, the switch modules 136 can include TDM and/or packetswitching engines.

Those of ordinary skill in the art will recognize the node 130 caninclude other components which are omitted for illustration purposes,and that the systems and methods described herein are contemplated foruse with a plurality of different network elements with the node 130presented as an example of a type of network element. For example, inanother embodiment, the node 130 may not include the switch modules 136,but rather have the corresponding functionality in the line modules 134(or some equivalent) in a distributed fashion. For the node 130, otherarchitectures providing ingress, egress, and switching are alsocontemplated for the systems and methods described herein. In general,the systems and methods described herein contemplate use with anynetwork element providing switching of channels, timeslots, tributaryunits, wavelengths, etc. and using the control plane 126, the SDNcontroller 128, etc. Furthermore, the node 130 is merely presented asone example of node 130 for the systems and methods described herein.

Controller

FIG. 7 is a block diagram of a controller 150 to provide control planeprocessing and/or OAM&P for the node 130. The controller 150 can be partof the common equipment, such as common equipment 132 in the node 130,or a stand-alone device communicatively coupled to the node 130 via theDCN 140. The controller 150 can include a processor 152 which is ahardware device for executing software instructions such as operatingthe control plane. The processor 152 can be any custom made orcommercially available processor, a central processing unit (CPU), anauxiliary processor among several processors associated with thecontroller 150, a semiconductor-based microprocessor (in the form of amicrochip or chip set), or generally any device for executing softwareinstructions. When the controller 150 is in operation, the processor 152is configured to execute software stored within the memory, tocommunicate data to and from memory 158, and to generally controloperations of the controller 150 pursuant to the software instructions.The controller 150 can also include a network interface 154, a datastore 156, memory 158, an I/O interface 160, and the like, all of whichare communicatively coupled to one another and to the processor 152.

The network interface 154 can be used to enable the controller 150 tocommunicate on the DCN 140, such as to communicate control planeinformation to other controllers, to the management system 138, to thenodes 130, and the like. The network interface 154 can include address,control, and/or data connections to enable appropriate communications onthe DCN 140. The data store 156 can be used to store data, such ascontrol plane information, provisioning data, OAM&P data, etc. The datastore 156 can include any of volatile memory elements (e.g., randomaccess memory (RAM, such as DRAM, SRAM, SDRAM, and the like)),nonvolatile memory elements (e.g., ROM, hard drive, flash drive, CDROM,and the like), and combinations thereof. Moreover, the data store 156can incorporate electronic, magnetic, optical, and/or other types ofstorage media. The memory 158 can include any of volatile memoryelements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM,etc.)), nonvolatile memory elements (e.g., ROM, hard drive, flash drive,CDROM, etc.), and combinations thereof. Moreover, the memory 158 mayincorporate electronic, magnetic, optical, and/or other types of storagemedia. Note that the memory 158 can have a distributed architecture,where various components are situated remotely from one another but maybe accessed by the processor 152. The I/O interface 160 includescomponents for the controller 150 to communicate with other devices.Further, the I/O interface 160 includes components for the controller150 to communicate with the other controllers/nodes, such as usingoverhead associated with TDM signals.

The controller 150 can be configured to communicate with othercontrollers 150 in the network 100 to operate the control plane 126 andfor control plane signaling. This communication may be either in-band orout-of-band. For SONET networks and similarly for SDH networks, thecontrollers 150 may use standard or extended SONET line (or section)overhead for in-band signaling, such as the Data Communications Channels(DCC). Out-of-band signaling may use an overlaid Internet Protocol (IP)network such as, for example, User Datagram Protocol (UDP) over IP. Inthe WDM network elements 124, the signaling can be via an OpticalService Channel (OSC). In an embodiment, the controllers 150 can includean in-band signaling mechanism utilizing OTN overhead. The GeneralCommunication Channels (GCC) defined by ITU-T Recommendation G.709 arein-band side channels used to carry transmission management andsignaling information within Optical Transport Network elements. Forexample, the GCC may be used for in-band signaling or routing to carrycontrol plane traffic. Based on the intermediate equipment's terminationlayer, different bytes may be used to carry control plane signaling.Other mechanisms are also contemplated for control plane signaling.

The controller 150 is configured to operate the control plane 126 in thenetwork 100. That is, the controller 150 is configured to implementsoftware, processes, algorithms, etc. that control configurable featuresof the network 100, such as automating discovery of the nodes, capacityon the links, port availability on the nodes, connectivity betweenports; dissemination of topology and bandwidth information between thenodes; path computation and creation for connections; network levelprotection and restoration; and the like. As part of these functions,the controller 150 can include a topology database that maintains thecurrent topology of the network 100 based on control plane signaling(e.g., HELLO messages) and a connection database that maintainsavailable bandwidth on the links 120 again based on the control planesignaling. The control plane 126 can be a distributed control plane;thus, a plurality of the controllers 150 can act together to operate thecontrol plane 126 using the control plane signaling to maintain databasesynchronization. In source-based routing, the controller 150 at a sourcenode 130 for a connection is responsible for path computation andestablishing by signaling other controllers 150 in the network 100, suchas through a SETUP message. Path computation generally includesdetermining a path, i.e., traversing the links 120 through the nodes 130from the originating node 130 to the destination node 130 based on aplurality of constraints such as administrative weights on the links,bandwidth availability on the links 120, etc.

Upshift/Downshift Process

In various embodiments, the systems and methods provide capacityadjustments in a modem 40 when the associated photonic service isrestored to a restoration route from a home route. Referring back toFIG. 5 , assume there is a photonic service 180 between the site 110 a,110 d with a home route 182 between the sites 110 a, 110 b, 110 d.Further, assume there is a failure or fiber cut (e.g., on a link 120, ora failure of components in the site 110 b), and there is a restorationroute 184 between the sites 110 a, 110 e, 110 d. As described herein,the home route 182 can be computed using various path computationtechniques and the photonic service 180 is instantiated in the network100 over the home route 182. At some point, the failure or fiber cutoccurs, and the controller 150 associated with the site 110 a (or someother component) can compute the restoration route 184 (alternatively,the restoration route 184) can be precomputed.

The foregoing flowcharts describe various processes for anupshift/downshift process to account for capacity differences (from anoptical perspective) of the home route 182 and the restoration route184. The systems and methods eliminate the strong dependency on marginprediction of the restoration route 184. As mentioned with respect tothe mesh network 30, paths can be complex in the mesh network 30, and itis difficult to have an accurate representation of optical margin (priorto installing the service, after which the margin can simply bemeasured). The mesh network 30 has many routes and many differentphotonic services with different A-Z routes, leading to a complexenvironment where system dynamics are constantly evolving.

Instead, the systems and methods provide an approach to utilize existingmargins after successful restoration. In other words, adapting theservice capacity to available margins to get home route capacity in thebest effort, a non-service affecting manner_(i.e., without impacting anyother copropagating services that may already be running with lowmargins and/or with upshifted capacity).

In the various flowcharts that follow, description is provided withreference to the photonic service 180 initially operating on the homeroute 182 which experiences a fault requiring restoration to therestoration route 184. While these processes are described withreference to a single photonic service 180, those of ordinary skill inthe art will realize a practical embodiment would include multiplephotonic services, each of which could be restored utilizing the systemsand methods described herein. Further, those of ordinary skill in theart will recognize various steps in the upshift and downshift processescan be used in combination with one another.

Upshift Process

FIG. 8 is a flowchart of an upshift process 200 for restoring a photonicservice from a home route to a restoration route with some insight intomargin available on the restoration route. The upshift process 200 isperformed in the network 100 after the photonic service 180 experiencesa fault on the home route 182, and after the control plane 126, the SDNcontroller, or some other entity determines the restoration route 184.Again, this determination of the restoration route 184 can be at runtime(when the fault occurs) or any time prior. The upshift process 200further includes some insight into the margin available on therestoration route 184. This insight can be based on measurements (e.g.,via equipment at the sites 110 a, 110 e, 110 d which monitor theassociated links 120), computation (e.g., estimates based on variablessuch as length of the links 120, optical parameters, etc.), and/or acombination of measurements and computation. That said, the insight intothe margin available can be an estimate (as is the case in thecomputation) or more accurate based on measurements.

The upshift process 200 includes, for a Layer 0 restoration, switchingto the restoration route 184 with a shift in capacity based on theavailable margin on the restoration route 184 (step 201). Here, themodems 40 forming the photonic service 180 can coordinate a shift incapacity downward if the available margin on the restoration route 184does not support the capacity of the photonic service on the home route182. Again, the photonic service 180 is formed by modems 40 that arecapable of supporting various capacity rates such as C₁, C₂, . . . ,C_(N), where C₁>C₂> . . . >C_(N). For example, the home route 182capacity can be C₁, and the restoration route 184 does not support thecapacity C₁ based on the insight into the available margin. At step 201,the photonic service 180 is shifted in capacity to some value C_(m)where m=2, 3, . . . , N and then the photonic service 180 is reroutedfrom the home route 182 to the restoration route 184. Of note, thisdownshift in the upshift process 200 is performed prior to rerouting.

In an embodiment, the insight into available margin on the restorationroute 184 can be an estimate or offline simulated and the downshift incapacity can be based on a conservative approach, i.e., a value which isexpected to work. Here, the downshift can be viewed as a “safe mode”where it is guaranteed that the photonic service 180 will operate on therestoration route 184. Note, often the restoration route 184 is longerthan the home route 182, which is why the home route 182 is selected asthe primary path. Here, the photonic service 180 is scaled back(downshifted) to a safe capacity prior to switching to the restorationroute 184. In this manner, there is no requirement to know the exactlyavailable margin on the restoration route 184. Rather, once the photonicservice 180 is on the restoration route 184, the upshift process 200includes upshifting to the next available capacity (C₁, C₂, . . . ) ifthe photonic service 180 is running error free with sufficient SNRmargin and with no possible impact on copropagating services on therestoration route 184 (step 202). Here, the photonic service 180operates in with the “safe” capacity on the restoration route 184initially and then upshifts as long as the photonic service 180 isrunning error free with sufficient SNR margin and with no possibleimpact on copropagating services on the restoration route 184.

Downshift Process

FIG. 9 is a flowchart of a downshift process 220 for restoring aphotonic service from a home route to a restoration route withoutinsight into margin available on the restoration route. The downshiftprocess 220 is similar to the upshift process 200, i.e., performed inthe network 100 after the photonic service 180 experiences a fault onthe home route 182, and after the control plane 126, the SDN controller,or some other entity determines the restoration route 184. Again, thisdetermination of the restoration route 184 can be at runtime (when thefault occurs) or any time prior. However, the downshift process 220 doesnot include some insight into the margin available on the restorationroute 184.

The downshift process 220, for a Layer 0 restoration, switching to therestoration route 184 with the home route capacity if the marginavailable on the restoration route 184 is not known in advance (step221). Note, while the upshift process 200 can be viewed as a “safe mode”approach, the downshift process 220 simply takes the approach to move tothe restoration route 184 and then downshift responsive to errors. Thatis, the downshift process 220 includes downshifting to the nextavailable capacity of the modem receiver fails to run error free andthere is no fault on the restoration route that can be correlated withthe failure (errors) (step 222).

Combined Upshift/Downshift Process

FIG. 10 is a flowchart of a process 250 including both upshifting anddownshifting of capacity when moving to a restoration route from a homeroute. The process 250 combines aspects of the upshift process 200, andthe downshift process 220. The process 250 is performed in the network100 after the photonic service 180 experiences a fault on the home route182, and after the control plane 126, the SDN controller, or some otherentity determines the restoration route 184, i.e., Layer 0 (LO)restoration (step 251). Again, this determination of the restorationroute 184 can be at runtime (when the fault occurs) or any time prior.The process 250 may or may not have insight into the margin available onthe restoration route 184 (step 252). If the process 250 includesknowledge of the margin on the restoration route 184 (step 252), theprocess 250 can include shifting capacity of the photonic service 180based on the available margin on the restoration route 184 and switchingthereto (step 253). This insight into margin can be based onmeasurements (e.g., via equipment at the sites 110 a, 110 e, 110 d whichmonitor the associated links 120), computation (e.g., estimates based onvariables such as length of the links 120, optical parameters, etc.),and/or a combination of measurements and computation. That said, theinsight into the margin available can be an estimate (as is the case inthe computation) or more accurate based on measurements.

If the process 250 does not have knowledge of the margin on therestoration route 184 (step 252), the process 250 includes switching tothe restoration route 184 with the home route 182 capacity (step 254).Once the photonic service 180 is on the restoration route 184, theprocess 250 includes monitoring the photonic service 180 to determine ifthere are any errors and what the SNR margin is and any impacts oncopropagating services along with the photonic service 180 (step 255).The errors can be determined from Bit Error Rate (BER) measurements,Forward Error Correction (FEC) Performance Monitoring (PM) data, etc.The SNR margin can also be determined based on various measurementsavailable during operation of the photonic service 180 over therestoration route 184.

Based on the results at step 255, the process 250 can include an upshiftin capacity (step 256) if the photonic service 180 is error free, hassufficient SNR, and causes no impact to copropagating services or adownshift in capacity (step 257) if the photonic service 180 has anyerrors, has insufficient SNR, and/or causes an impact to copropagatingservices.

In an embodiment, the upshift and downshift in capacity can be done indiscrete increments. For example, the capacity can be any of C₁, C₂, . .. , C_(N), where C₁>C₂> . . . >C_(N) and the downshift includes movingfrom C_(M) to C_(M−1), and the upshift includes moving from C_(M) toC_(M+1). Of course, the upshift can include exceeding the capacity onthe home route 182. However, more likely, the objective of the upshiftis to get as close as possible to the capacity on the home route 182while on the restoration route 184. In another embodiment, the upshiftand downshift in capacity can be done in analog increments.

Detailed Upshift Process

FIG. 11 is a flowchart of a detailed upshift process 300 which providesadditional details of the upshift process 200. The detailed upshiftprocess 300 assumes the modems 40 for the photonic service 180 arecapable of supporting variable capacity and the viable capacity of therestoration route(s) are known or predicted in advance (step 301). Asdescribed herein, viable capacity means the margin is known orpredicted, and a determination can be made as to what capacity can besupported on the restoration route 184, i.e., the viable capacity.

The photonic service 180 is operating on the home route 182, and theprocess 300 initiates responsive to a fault on the home route 182 (step302). A restoration route 184 is determined/found with availablebandwidth for the restoration of the photonic service 180 (step 303).Again, this determination of the restoration route 184 can be at runtime(when the fault occurs) or any time prior. With respect to availablebandwidth, this generally implies the photonic service 180 can supportthe same capacity on the restoration route 184 as on the home route 182.In an embodiment, the determined restoration route 184 can be foundbased on this assumption. However, in practice, there may becircumstances where it is not possible to match the capacity. As statedherein, often, one of the available restoration routes 184 may have morelink budget constraints than the home route 182 which means there may beless margin. Such link budget constraints may include longer distance,impaired or degraded fiber spans, different fiber types, more OADMcounts or filter penalties, penalties from optical amplifications and soon. This is also more likely in larger, complex, mesh optical networkswhere there are multiple photonic services and any fault causes the needfor multiple restoration routes. The various systems and methodsdescribed herein provide an ability to provide best effort capacity.

The process 300 includes determining if the photonic service 180'scapacity on the restoration route 184 is less than the home routecapacity (step 304). As described herein, this determination is based onthe viable capacity on the restoration route 184. If so, the photonicservice 180 is downshifted to some restoration capacity which is lessthan the home route 182 capacity (step 305). If the photonic service180's capacity on the restoration route 184 is greater than or equal tothe home route capacity or after the downshift in step 305, the photonicservice 180 is switched to the restoration route 184 (step 306). Theprocess 300 includes waiting until the photonic service 180 is addedsuccessfully, in both directions (for bidirectional communication) onthe restoration route 184 (step 307).

Once the photonic service 180 is operating on the restoration route 184,measurements can be determined, and it can be determined if the photonicservice is operating error-free (step 308). If there are errors (step308), the process 300 can determine if there are any faults detected onthe restoration route 184 (step 309). If there are no faults on therestoration route 184, the photonic service 180 has been downshifted asmuch as possible, and there are still errors on the photonic service180, then the restoration fails (step 310). Optionally, there can beanother determination of an alternate restoration route. However, it istypically assumed here that the restoration route 184 was selected asbeing a shortest route and any alternate restoration route would belonger and thus also experience errors. If there is a fault detected onthe restoration route 184 (step 309), the process 300 can includefinding a next shortest available restoration route (step 311) andreturning to step 304.

Back at step 308, if the photonic service 180 is operating error-free onthe restoration route 184 (step 308), the process 300 includesdetermining if the photonic service 180 is operating currently on therestoration route 184 at the home route 182 capacity (step 312). If so,the process 300 ends as restoration is complete (step 313). If thephotonic service 180 is not at the home route capacity (step 312), theprocess 300 includes determining if the SNR margin is greater than anupshift threshold (step 314). The upshift threshold means there isenough margin for the photonic service 180 to move to a higher capacity.If there is not enough margin (step 314), the process 300 ends asrestoration is complete (step 313).

If there is enough margin (step 314), the process 300 includes checkingif an upshift would impact any copropagating services (step 315). Ifthere is an impact (step 315), the process 300 ends as restoration iscomplete (step 313). If there is no impact (step 315), the process 300includes upshifting the line rate of the photonic service 180 (step 316)and waiting until the capacity shift is completed successfully (step316) before returning to step 308.

Detailed Downshift Process

FIG. 12 is a flowchart of a detailed downshift process 400 whichprovides additional details of the downshift process 220. The detaileddownshift process 400 assumes the modems 40 for the photonic service 180are capable of supporting variable capacity, and the viable capacity ofthe restoration route(s) is not known or predicted in advance (step401). The photonic service 180 is operating on the home route 182, andthe process 400 initiates responsive to a fault on the home route 182(step 402). A restoration route 184 is determined/found with availablebandwidth for the restoration of the photonic service 180 (step 403).The photonic service 180 is switched to the restoration route 184 withthe home route capacity (step 404). The process 400 includes waitinguntil the photonic service 180 is added successfully in both directions(step 405).

At this point, measurements are determined, and it is determined if thephotonic service 180 is operating error-free on the restoration route184 (step 406). If the photonic service 180 is operating error fee (step406), the process 400 ends as restoration is complete, i.e., thephotonic service 180 is operating error-free at the home route capacityon the restoration route 184 (step 407). If the photonic service is noterror-free (step 406), the process 400 includes determining if there areany faults detected on the restoration route 184 (step 408). If thereare faults detected (step 408), the process 400 includes determining anext shortest restoration route (step 409) and returning to step 404.

If there are no faults (step 408), the process 400 includes determiningwhether the modems 40 for the photonic service 180 are at a minimumcapacity (step 410). If so, the process 400 ends as the restorationfails (step 411). If the modems 40 are not at the minimum capacity (step410), the process 400 includes downshifting the capacity of the photonicservice 180 (step 412), waiting until the photonic service 180 isdownshifted successfully (step 413), and returning to step 406.

Determination of an Upshift Capability

FIG. 13 is a flowchart of an upshift capability process 500 whichdetermines the margin and possibility of an upshift in theaforementioned processes. The process 500 is performed after thephotonic service 180 is up and operating on the restoration route 184.The process 500 includes obtaining BER values from modems 40 at bothends of the photonic service over a certain duration T followingrestoration (step 501). This can be by directly measuring modem BER atboth ends (modems 40) of a bidirectional photonic service 180. Note, inoptical regenerator(s) are inline, then the measurement is from each ofthe modems 40 including ones at the optical regenerator(s).

The process 500 includes obtaining the BER value at which there is aSignal Fail (SF) (step 502). For example, the SF can be when there is aLoss of Clock at an Rx. The process 500 also includes obtaining the BERvalue at which there is a Signal Degrade (SD) (step 503). SD is a pointat which, below, the Rx may see periodic errors.

SF is a threshold point at which the FEC can no longer converge on someframes and produces an overflow, sometimes called FEC overflow. SD is asofter threshold which can be set by the user or the system whichrepresents the point at which the FEC is still operating properly, butthe output BER is above a required threshold, e.g., 10⁻¹⁵ or 10⁻¹². FECcan be viewed as a function with an input BER and an output BER,pre-FEC-BER and post-FEC-BER, respectively. The values for BER for SFand SD can be retrieved from the modem 40 since each modem 40 may havesettings as calibrated during factory calibration. It is also possiblethat the user or other external applications may provision the SDthreshold value higher than what modem, in default is capable ofRegardless, the values are retrieved from the modems 40 on both ends inreal-time. Signal Degrade can be set at an arbitrary additional marginthreshold above a FEC overflow point.

Next, the process 500 includes converting the BER values above to SNR(step 504). The BER from each modem Rx can be converted to SNR using agraph as shown for a given line rate or transmission mode (combinationof line rate, modulation, and Baud rate). FIG. 14 is a graph of anexample photonic service illustrating SNR in dB versus Bit Error Rate(BER) for different capacity rates, namely 100G, 200G, 300G, 400G.

The BER to SNR conversion chart can be pre-determined using factorycalibrated charts with back-to-back to conversion. For example, if themeasured BER for a modem Rx at 200G line rate is 10⁻⁵, then according tothe graph, the measured SNR on that modem Rx will be 14.5 dB. If thepre-FEC signal fail threshold is 3.40×10⁻⁰² (this is the default SFthreshold for an example modem at 56GBaud 200 Gbps line rate), then theSNR at which the signal will fail, i.e., Rx will not be able to performany more FEC correction, will be 7 dB. The difference between measuredcurrent SNR and the SNR at which signal will fail gives the SNR marginfor that modem in receiving direction at the given capacity. In thiscase, it will be 7.5 dB SNR margin at 200G line rate.

For each bi-directional photonic service, there is at least 2×SNR margindata—one for the forward direction, and one for the reverse direction.If there are regenerators involved, then there will be 2× extra SNRmargin data points available for each regenerator banks. If a photonicservice is delivered using paired modems such as a 300 Gbps capacity canbe delivered using 2×150 Gbps modems, where each modem is sharing aportion of the total photonic capacity, then there will be at least2×SNR margin data points for each of those modem pairs (forward/reversedirection).

To get the minimum SNR margin for a photonic service (step 505), the SNRis tracked over time T, and a time-series lower bound can be determinedusing an appropriate probability of occurrence. The minimum of thetime-series lower bound from each direction can provide the minimum SNRmargin value for a given photonic service, which is then considered asthe effective SNR margin of the photonic service and later used forchecking upgrade capability.

The process 500 includes determining the margin which is the SNR at thecurrent capacity minus the SNR at SF (step 506). The process 500includes determining the SNR to overcome SD at the next capacity levelsupported by the modem (step 507). In order to check for upgradecapability, the SNR required to overcome the signal degrade threshold atthe next capacity is determined. This is performed by knowing the signaldegrade pre-FEC BER threshold for a modem which is the same for anygiven line rate or transmission mode. The SD pre-FEC BER threshold isconverted to SNR using the BER to SNR conversion chart for the nextavailable line rate. In this example (FIG. 14 ), it will be 11.5 dB SNRat 300 Gbps line rate for an SD pre-FEC BER threshold of 2.66×10⁻⁰².Since the current SNR for the service is measured as 14.5 dB which ishigher than the required SNR to overcome signal degrade condition at thenext available line rate, the service will be considered upgrade capablefrom its current line rate or capacity of 200 Gbps to the next line rateor capacity 300 Gbps. That is, if the minimum SNR at the currentcapacity is greater than the required SNR to overcome SD at the nextcapacity level, then the photonic service 180 is upshift capable (step508).

SNR Calculation

The modems 40 provide measurements of BER. Q has a simple relationshipto BER and is further simplified by only using the one for QuadraturePhase Shift Keying (QPSK). SNR has a slightly more complicatedrelationship to BER. Therefore, Q has a complicated relationship withSNR. SNR has a simple relationship to margin and to capacity which iswhy it is more useful than Q. Q was used in the past because it issimpler to calculate than SNR and behaves similarly in many cases.Essentially, Q used to be a convenient approximation for SNR. However, Qis defined differently for each modulation format. For this reason, itis generally simplified to use the Q for QPSK for all formats.

There are also analytic formulas for conversion from SNR to pre-FEC-BERfor simple formats like Binary Phase Shift Keying (BPSK), QPSK, etc. Thefollowing is the equation for QPSK.

${preFECBER} = {\frac{1}{2}{{erfc}\left( \sqrt{\frac{1}{2}{SNR}} \right)}}$

One can use this to convert from BER to SNR using a simple numericalsolver. However, for many modulation formats, there are no analyticalforms (that are simple to derive), so empirical curves derived from asimulation can be used. One could use factory calibration curves as analternative. The advantage that the simulations have over the factorycalibration is that the curves can be created for a “noiseless”receiver. This means that the implementation penalty of the receiver inthe field is part of the SNR that gets reported.

In the network 100, there can be an external service that monitors SNRmargin. This external service can be implemented on the controller 150,on the modem 40, distributed, etc. On restoration (similar to theirrecovery), the processes can utilize time-varying SNR margin (i.e.,average SNR over time) to decide if the service itself is upshiftcapable as well as paying attention to the margins of all co-propagatingservices, before a decision to upshift.

SNR Margins for Other Photonic Services Sharing a Path

FIG. 15 is a flowchart of a process 600 for determining SNR margins forother photonic services sharing the same path as the photonic service180. The process 600 is utilized along with the process 500 to determineupshift capability of the photonic service 180. The foregoing upshiftprocesses avoid an upshift of the photonic service 180 if there isinsufficient margin for the photonic service 180 AND if there could bean impact to other copropagating services. This second condition isimplemented to avoid adverse effects on other services.

The process 600 includes, on an optical path of interest which is therestoration route 184 of the photonic service 180, for each direction(transmit and receive), determining all photonic services over theoptical path of interest (step 601). This can be performed bydetermining all fiber spans on the optical path of interest; for eachfiber span, determining all the photonic services are running throughthat are currently occupying the spectrum; and performing a union of theset of services running on all fiber spans that will provide the list ofall other services sharing the same path.

The process 600 includes determining SNR margin for all the photonicservices (step 602). This can be performed as described above withreference to the process 500. The process 500 includes determining ifany of the photonic services has a margin below a pre-determinedthreshold (step 603). If no photonic service over the optical path ofinterest is below the margin threshold (step 603), the photonic service180 is upshift capable (step 604) assuming the photonic service 180 hassufficient margin per the process 500. If one or more photonic servicesover the optical path of interest is below the margin threshold (step603), the photonic service 180 is not upshift capable (step 605). Ofcourse, this assumption in step 605 can be modified, allowing someimpact, etc.

It will be appreciated that some embodiments described herein mayinclude one or more generic or specialized processors (“one or moreprocessors”) such as microprocessors; Central Processing Units (CPUs);Digital Signal Processors (DSPs): customized processors such as NetworkProcessors (NPs) or Network Processing Units (NPUs), Graphics ProcessingUnits (GPUs), or the like; Field Programmable Gate Arrays (FPGAs); andthe like along with unique stored program instructions (including bothsoftware and firmware) for control thereof to implement, in conjunctionwith certain non-processor circuits, some, most, or all of the functionsof the methods and/or systems described herein. Alternatively, some orall functions may be implemented by a state machine that has no storedprogram instructions, or in one or more Application Specific IntegratedCircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic or circuitry. Ofcourse, a combination of the aforementioned approaches may be used. Forsome of the embodiments described herein, a corresponding device inhardware and optionally with software, firmware, and a combinationthereof can be referred to as “circuitry configured or adapted to,”“logic configured or adapted to,” etc. perform a set of operations,steps, methods, processes, algorithms, functions, techniques, etc. ondigital and/or analog signals as described herein for the variousembodiments.

Moreover, some embodiments may include a non-transitorycomputer-readable storage medium having computer readable code storedthereon for programming a computer, server, appliance, device,processor, circuit, etc. each of which may include a processor toperform functions as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, an optical storage device, a magnetic storage device, a ROM(Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM(Erasable Programmable Read Only Memory), an EEPROM (ElectricallyErasable Programmable Read Only Memory), Flash memory, and the like.When stored in the non-transitory computer-readable medium, software caninclude instructions executable by a processor or device (e.g., any typeof programmable circuitry or logic) that, in response to such execution,cause a processor or the device to perform a set of operations, steps,methods, processes, algorithms, functions, techniques, etc. as describedherein for the various embodiments.

Although the present disclosure has been illustrated and describedherein with reference to preferred embodiments and specific examplesthereof, it will be readily apparent to those of ordinary skill in theart that other embodiments and examples may perform similar functionsand/or achieve like results. All such equivalent embodiments andexamples are within the spirit and scope of the present disclosure, arecontemplated thereby, and are intended to be covered by the followingclaims.

What is claimed is:
 1. A node comprising: an optical modem configured toconnect to an optical network and to provide a photonic service in theoptical network, wherein the optical modem is capable of supportingvariable capacity; and a controller communicatively connected to theoptical modem and configured to detect a fault or receive notificationof the fault on a current route of the photonic service while thephotonic service operates at a first capacity of the variable capacitycause a change of the optical modem to a second capacity of the variablecapacity, subsequent to the fault, wherein the optical modem isconfigured to switch to a restoration route while the optical modemoperates at the second capacity, and monitor operation on therestoration route for a possible change in the second capacity and causea change of the optical modem to a third capacity of the variablecapacity based on the monitored operation, wherein the second capacityand the third capacity are based on any impact to margin of othercopropagating services on the restoration route, wherein the possiblechange is based on measured margin of the photonic service and the othercopropagating services.
 2. The node of claim 1, wherein the photonicservice is monitored based on measurements of Bit Error Rate (BER) ofthe photonic service on the restoration route to determine the margin interms of Signal-to-Noise Ratio (SNR).
 3. The node of claim 1, whereinthe photonic service is changed if the margin is higher than margin toovercome a signal degrade condition.
 4. The node of claim 1, wherein thesecond capacity is based on known viable capacity on the restorationroute.
 5. The node of claim 1, wherein the second capacity is based onpredicted viable capacity on the restoration route.
 6. The node of claim1, wherein the variable capacity is configured in discrete increments.7. The node of claim 1, wherein the impact on the other copropagatingservices is determined based on whether the other copropagating servicesare already running with low margins and are with upshifted capacity. 8.The node of claim 1, wherein the first capacity and the second capacityare different.
 9. The node of claim 1, wherein the first capacity andthe second capacity are the same.
 10. A node comprising: an opticalmodem configured to connect to an optical network and to provide aphotonic service in the optical network, wherein the optical modem iscapable of supporting variable capacity; and a controllercommunicatively connected to the optical modem and configured to detecta fault or receive notification of the fault on a current route of thephotonic service while the photonic service operates at a first capacityof the variable capacity, subsequent to a switch to a restoration route,monitor operation on the restoration route, cause a change of theoptical modem to a second capacity of the variable capacity based on themonitored operation on the restoration route, and monitor operation onthe restoration route for a possible change in the second capacity andcause a change of the optical modem to a third capacity of the variablecapacity based on the monitored operation, wherein the second capacityand the third capacity are based on any impact to margin of othercopropagating services on the restoration route, wherein the possiblechange is based on measured margin of the photonic service and the othercopropagating services.
 11. The node of claim 10, wherein the photonicservice is changed is to a lower capacity when the photonic servicefails to run error free on the restoration route.
 12. The node of claim10, wherein the photonic service is monitored based on measurements ofBit Error Rate (BER) of the photonic service on the restoration route todetermine the margin in terms of Signal-to-Noise Ratio (SNR).
 13. Thenode of claim 10, wherein the impact on the other copropagating servicesis determined based on whether the other copropagating services arealready running with low margins and are with upshifted capacity.
 14. Amethod comprising: detecting a fault or receive notification of thefault on a current route of a photonic service while the photonicservice operates at a first capacity, wherein the photonic service isprovided via an optical modem capable of supporting variable capacity;changing the optical modem to a second capacity of the variablecapacity, subsequent to the fault; switching the optical modem to arestoration route while the optical modem operates at the secondcapacity; and monitoring operation on the restoration route for apossible change in the second capacity and cause a change of the opticalmodem to a third capacity of the variable capacity based on themonitored operation, wherein the second capacity and the third capacityare based on any impact to margin of other copropagating services on therestoration route, wherein the possible change in based on measuredmargin of the photonic service and the other copropagating services. 15.The method of claim 14, wherein the photonic service is monitored basedon measurements of Bit Error Rate (BER) of the photonic service on therestoration route to determine the margin in terms of Signal-to-NoiseRatio (SNR).
 16. The method of claim 15, wherein the photonic service ischanged if the margin at the second capacity is higher than an SNRmargin to overcome a signal degrade condition.
 17. The method of claim14, wherein the second capacity is based on known viable capacity on therestoration route.
 18. The method of claim 14, wherein the secondcapacity is based on predicted viable capacity on the restoration route.19. The method of claim 14, wherein the variable capacity is configuredin discrete increments.
 20. The method of claim 14, wherein the impacton the other copropagating services is determined based on whether theother copropagating services are already running with low margins andare with upshifted capacity.